Gas Phase Reactions of - ACS Publications - American Chemical

8 Gas Phase Reactions of N,N-Dimethylhydrazine with Ozone and NO in Simulated Atmospheres x

Facile Formation of N-Nitrosodimethylamine

Downloaded by UNIV OF GUELPH LIBRARY on May 15, 2012 | http://pubs.acs.org Publication Date: December 9, 1981 | doi: 10.1021/bk-1981-0174.ch008

WILLIAM P. L. CARTER, ERNESTO C. TUAZON, ARTHUR M. WINER and J. N. PITTS, JR. Statewide Air Pollution Research Center, University of California, Riverside, CA 92521 The gas phase reactions of unsymmetrical dimethylhydrazine (UDMH) with ozone and with NO have been studied under simulated atmospheric conditions i n a 30,000-liter outdoor Teflon chamber using in - s i t u long path Fourier transform infrared spectros copy. The reaction of UDMH with O (at ppm levels) i n a i r goes to completion i n less than 2 minutes forming N-nitrosodimethylamine as the predominant product (≥60% yield) along with smaller amounts of HCHO, H O , and HONO. In pureair,UDMH undergoes a slow dark reaction with the only product detected being NH at low yields. The UDMH decay rate i s unaffected by the addition of NO, but instead of NH , formation of HONO, N O, and one or more unidentified products are observed. When a UDMH-NO-air mixture i s irradiated, N-nitrosodimethylamine, N-nitrodimethylamine, HCHO, N O, and unknown product(s), believed to be primarily N-nitrosodimethylhydrazine, are formed. The unknown products are formed only during the initial stages, and the nitramine i s formed only during the later stages of the irradi ation. Possible mechanisms which are consistent with the observed data for the UDMH + O and UDMH + NO systems are discussed. 3

2

2

3

3

2

2

3

U n t i l recently the atmospheric chemistry of nitrogencontaining compounds such as the hydrazines, which are widely used as fuels i n m i l i t a r y and space vehicles, has received comparatively l i t t l e attention. Ν,Ν-dimethylhydrazine (also UDMH = unsymmetrical dimethylhydrazine) i s used i n liquid-fueled rockets, and thus there i s a p o s s i b i l i t y that i t s use, storage, and handling could result i n i t s release i n the atmosphere. There i s evidence that N-nitrosodimethylamine can be among i t s oxidation products ÇL-3) but, other than studies of the gas phase 0097-6156/81/0174-0117$05.00/0 © 1981 American Chemical Society In N-Nitroso Compounds; Scanlan, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

118

N-NITROSO COMPOUNDS

s t a b i l i t y of UDMH at r e l a t i v e l y high concentrations (2-4), there have been r e l a t i v e l y few investigations of i t s atmospheric reactions. In view of i t s potential for nitrosamine formation, a more detailed knowledge of the atmospheric reactions and products of UDMH i s clearly desirable. In order to provide such data for UDMH and other hydrazines we have studied their dark reactions i n a i r , with and without added 0 or NO, and have investigated their atmospheric photooxidation i n the presence of NO (5,6). In this paper, we report the results we have obtained to date for UDMH. Downloaded by UNIV OF GUELPH LIBRARY on May 15, 2012 | http://pubs.acs.org Publication Date: December 9, 1981 | doi: 10.1021/bk-1981-0174.ch008

3

Experimental The f a c i l i t y , methods of procedure, and materials employed i n this study have been discussed i n d e t a i l elsewhere (5>6), and are only b r i e f l y described here. The outdoor reaction chamber employed i n this study consists of a 30,000-liter FEP-type Teflon bag of triangular cross section held semi-rigidly by a framework of s t e e l pipes. The chamber houses a set of multiple-reflection optics (capable of pathlengths i n excess of 1 km) which i s i n t e r faced to a Midac interferometer and associated data system. Measured amounts of the reactants i n glass bulbs (for UDMH and 0 ) or glass syringes (for NO) were flushed into the chamber by a stream of N through a disperser tube which runs the length of the chamber. Fans attached to the Teflon-coated aluminum end panels provide rapid mixing of reactants. For dark experiments, the chamber was covered with an opaque tarpaulin; the l a t t e r could be removed readily for sunlight i r r a d i a t i o n s . The chamber was thoroughly flushed with clean ambient a i r after each run, and was additionally purged and f i l l e d with a t o t a l of five volumes of purified a i r (7) prior to each experiment. N i t r i c oxide (NO) and nitrogen dioxide (N0 ) were monitored by a Bendix chemiluminescence instrument. However, since the N0 " readings of this type of instrument are known to include the contribution of HN0 , HONO, PAN, and other organic nitrates (8), we report these readings as "gaseous n i t r a t e . " The growth and decay of a l l other species (including 0 ) were monitored by Fourier transform infrared (FT-IR) spectroscopy at a t o t a l pathlength of 460 meters and a spectral resolution of 1 cm" . At this pathlength, the intense absorptions of H 0 and CO l i m i t the usable IR spectral windows to the approximate regions 750-1300, 2000-2300, and 2400-3000 cm" . Each spectrum (700-3000 cm" ) was adequately covered by the response of the Cu:Ge detector. Approximately 40 seconds were required to collect the 32 interferograms co-added for each spectrum. Reactant and product analyses were obtained from the inten s i t i e s of infrared absorption bands by successive subtraction of absorptions by known species. Low noise reference spectra for UDMH and several reaction products were generated for this pur pose i n order to minimize the increase i n the noise l e v e l of the residual spectrum with each stage of subtraction. 3

2

2

ff

2

3

3

1

2

1

1

In N-Nitroso Compounds; Scanlan, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

8. CARTER ET AL.

Formation

of

N-Nitrosodimethylamine

119

Results and Discussion Dark Decay of UDMH i n A i r . UDMH was observed to undergo a gradual dark decay i n the 30,000-liter Teflon chamber at a rate which depended on humidity. S p e c i f i c a l l y , at 41°C and 4% RH the observed UDMH h a l f - l i f e was ~9 hours ( i n i t i a l UDMH =4.4 ppm) and at 40°C and 15% RH, the h a l f - l i f e was -6 hours ( i n i t i a l UDMH «2.5 ppm). The only observed product of the UDMH dark decay was NH , which accounted for only -5-10% of the UDMH l o s t . In par t i c u l a r , no nitrosamine, nitramine, or hydrazone were observed. Formaldehyde dimethylhydrazone was observed i n previous studies which employed higher UDMH concentrations and reaction vessels with r e l a t i v e l y high surface/volume ratios (2,4). The mechanism of the UDMH dark decay i s unknown, but i t i s presumed to be heterogeneous i n nature. I t i s probably not wall adsorption, since much slower decay rates were observed previ ously i n the absence of 0 (4).


3

2

Dark Reaction of UDMH with Oq. When O3 was injected into UDMH-air mixtures, consumption of UDMH and O3 was "instantaneous" and formation of N-nitrosodimethylamine was immediately observed. The reaction was complete within 2 minutes, by which time either the hydrazine or the O3 was t o t a l l y consumed. Figure 1 shows IR spectra before and 2 minutes after -2 ppm of O3 was injected into a i r containing -2 ppm of UDMH. The nitrosamine i s p o s i t i v e l y i d e n t i f i e d by i t s IR absorptions at 1296, 1016, and 848 cm" . Also formed i n the UDMH-03 system, but i n lesser y i e l d s , were HCHO, H 0 , and H0N0. The experimental conditions and products observed at selected times i n the UDMH + O3 experiments are shown i n Table I. In general, the nitrosamine yields ranged from -60% when the reaction was carried out i n a s l i g h t excess of UDMH to -100% when 0 was i n excess. The HCHO, H 0 , and HONO yields were -13%, 10%, and 3% of the reacted UDMH when near-stoichiometric mixtures were employed. N0 was probably also formed to some extent, but the interference by other nitrogenous compounds on the NOj* analyzer (8) made the determination of i t s exact y i e l d uncertain. The observed O3/UDMH stoichiometry was -1.5:1. The data are consistent with the following mechanisms for the UDMH-O3 reaction: 1

2

2

3

2

2

2

(CH ) N-NH + 0 3

2

2

(CH ) N-NH + OH 3

2

2

(CH ) N-NH + 0 3

2

(CH ) N-NH + OH + 0

3

3

3

2

—>

(CH ) N-NH + H 0

—>

(CH ) N-N;

3

3

2

2

2

(2)

2

+0

(1)

2


(3)


a

2

e

d

3

C

3

2

2

2

2

2

3

3

2

3

2

2

Concentrations (ppm) Elapsed "Gaseous, Time (CH ) NN0 HONO Nitrate" HCHO NH (CH ) NNO H 0 UDMH 0 (min) 0.116 0.02 1.71 -7 INJECTED -2.0° 0 10 1 21 0.14 0.19 0.106 0.023 0.81 0.386 — 2 — 0.08 0.08 0.079 0.062 0.92 0.78 0.170 — 61 — + START OF SUNLIGHT IRRADIATION (1401 PDT, May 9, 1980) 69 0.34 0.077 0.19 0.86 0.15 0.07 0.41 — — 79 0.68 0.48 0.50 — — — — 0.51 128 0.116 0.106 1.93 -9 ~2.0 + INJECTED 0 10 21 2 0.82 0.13 0.17 0.099 0.479 — 3 — — 0.045 0.051 0.069 0.052 0.83 0.77 0.293 — —— 73 -2.0° + INJECTED 84 — 0.066 1.42 0.13 0.21 1.09 — 1.47 88 0.22 — 0.058 1.22 0.15 1.11 — 1.09 120 Dash means below FT-IR detection s e n s i t i v i t y ; blank means no measurement was made. "Gaseous n i t r a t e " i s t o t a l amount of species converted to NO by the molybdenum catalyst of a commercial ΝΟ-ΝΟχ analyzer (8). This includes N0 , HONO and organic n i t r a t e s , and possibly nitros amines and nitramines. Calculated amount injected. a d d i t i o n a l products observed at end of i r r a d i a t i o n : CO (0.9 ppm), CH 0N0 (0.05 ppm), HCOOH (0.043 ppm), N 0 (0.035 ppm). a d d i t i o n a l products detected at end of run: CO (0.3 ppm), N 0 (0.033 ppm).

Conditions RH Exp. Τ (avg) No. (avg) (%)

3

Table I. Experimental Conditions and Concentrations of Reactants and Products at Selected Times i n the UDMH + 0 Dark Experiments


8. CARTER ET AL.

Formation

(CH ) N 3

+ 0

2

2

of N-Nitrosodimethylamine

—>

(CH ) N-NO + H0

—>

H 0 +0

3

2

121

(4)

2

Ή H0 + H0 2

2

2

2

(5)

2

Other possible mechanisms have been considered (5), but they either predict formation of products which are not observed, do not explain the observed 0 /UDMH stoichiometry, or are inconsis tent with the results of the UDMH-NO stoichiometry and the f o r mation of nitrosamine and H 0 i n this system. The other pro ducts observed, and the fact that the nitrosamine and H 0 yields are somewhat less than the predicted 100% and 50% of the UDMH consumed, can be attributed to possible secondary reactions of the nitrosamine with the OH r a d i c a l . It should be noted that the UDMH + 0 mechanism i s probably quite different from that appropriate for hydrazines with hydro gens on both nitrogen atoms. In our study of the reactions of O3 with N H^ and monomethyl hydrazine (MMH) (.5,6) , the data were best explained by assuming the i n i t i a l hydrazine consumption reactions to be analogous to reactions (1) and (2), but with the N-amino r a d i c a l formed reacting rapidly with 0 , e.g.,


3

2

2

2

2

3

2

2

CH3NH-NH + 0

—>

2

CH N=NH + H 0 3

2

(6)

to give r i s e to products other than nitrosamines. Since a reac tion analogous to (6) i s not possible for UDMH, i t s mechanism and products are s i g n i f i c a n t l y different. Irradiation of the UDMH 4- O3 Reaction Products. One experi ment was conducted i n which the UDMH + O3 reaction products (with UDMH i n s l i g h t excess) were irradiated by sunlight. The results are shown i n Table I and Figure 1. I t can be seen that rapid consumption of UDMH, the nitrosamine, and HONO occurred, with Nnitrodimethylamine (also dimethylnitramine) and additional form aldehyde being formed. The formation of nitramine upon i r r a d i ation of the nitrosamine i s consistent with results of previous studies i n our laboratories (9^,10), and probably occurs as shown: (CH ) N-N0 + hv — > 3

2

(CH ) N« + N 0 3

2

2

—>

(CH ) N» + NO

(7)

(CH ) N-N0

(8)

3

2

3

2

2

It should be noted that the immediate formation of the nitramine i n the photolysis of the UDMH + O3 products indicates the presence of N 0 i n that mixture. 2



122

N-NITROSO COMPOUNDS

-J

800

I

I

I

1000

I

1200

L

FREQUENCY (cm" ) 1

Figure 1. Selected IR spectra from the UDMH + O experiments (NH absorptions subtracted): (a) UDMH prior to O injection; (b) 2 min after O injection; (c) approximately 1 h into sunlight irradiation of reaction mixture. s

s

S

s


8. CARTER ET AL.

Formation

of

^-Nitrosodimethylamine

123

Dark Decay of UDMH i n the Presence of NO. When 1.3 ppm of UDMH i n a i r was reacted i n the dark with an approximately equal amount of NO, -0.25 ppm of UDMH was consumed and formation of -0.16 ppm HONO and -0.07 ppm N 0 was observed after -3 hours. Throughout the reaction, a broad infrared absorption at -988 cm*" corresponding to an unidentified product(s), progressively grew i n intensity. The residual infrared spectrum of the unknown product(s) i s shown i n Figure 2a. I t i s possible that a very small amount (

2

S

(CH ) N-NH + NO 3

2

(15)

H

which can account for the rapid disappearance of the unknown once the UDMH i s consumed. On the other hand, the nitrohydrazine, l i k e nitramines, should be more stable under i r r a d i a t i o n than i s the unknown product observed here. Thus the unknown product i s probably primarily nitrosohydrazine. Consistent with this con clusion i s the fact that the N0 levels are quite low compared to that of NO during the i n i t i a l stage, as indicated by the low "gaseous n i t r a t e " readings (Table II) and the low amount of nitramine formed. The r e l a t i v e l y high concentrations of HONO observed during the i n i t i a l period can be attributed to high OH and NO l e v e l s , with HONO being i n photostationary state due to i t s rapid photolysis (11). 2

OH + NO — > HONO + hv

HONO

(16)

> OH + NO

(17)

From the prevailing NO and HONO levels occurring during this period of the i r r a d i a t i o n , the HONO photolysis rate (11,14), and the rate constant for the OH + NO reaction (15), we estimate that steady state OH levels of -2 χ 10 molecule cm" were present. From this OH r a d i c a l concentration and assuming an UDMH + OH rate constant similar to those observed for N H^ and MMH (.5,16) , we calculate a UDMH decay rate which i s i n reasonable agreement with what i s observed. Thus, the HONO l e v e l measured during the i n i t i a l period i s entirely consistent with our assumed mechanism. The sudden consumption of the remaining UDMH, and the increased r e l a t i v e importance of N-nitrosamine formation at -30 minutes into the photolysis can be rationalized by assuming that at that time the [N0 ]/[N0] r a t i o , and thus the photostationary state [ 0 ] , has become s u f f i c i e n t l y high that 0 may be reacting with the hydrazine d i r e c t l y , and that reaction (3) begins to dominate over reaction (10). This results i n higher rates of UDMH consumption by the OH radicals formed i n the UDMH + 0 reac tion (1), and by the OH radicals generated by the reaction of NO 7

3

2

2

3

3

3


8.

CARTER ET AL.

Formation

of

129

^-Nitrosodimethylamine

with the HO2 r a d i c a l (resulting from reactions 3 and 4): H0

+ NO —>

2

OH + N0

(18)

2

Reaction (18) also converts NO to N0 which further increases the 0 l e v e l s , thus accelerating the overall process. The formation of the other products observed during the i r r a d i a t i o n can be attributed to secondary reactions. For example, formation of N 0, HCHO, and traces of CH30N0 (Table I I ) may result from the reaction of the nitrosamine with OH: 2

3


2

2

•CH N-NO + H 0 CH '

(19)

*0 CH N-NO CH '

(20)

2

(CH ) N-NO + OH 3

>

2

s

2

3

•CH

2 X

2

N-NO + 0 CH '

—>

2

3

•0 CH 2

2 v

3

OCH

2

X

N-N0 + NO CH '

>

3

2

V

N-N0 + N0 CH '

(21)

2

3

•0CH

2 N

N-N0 CH '

> HCHO + CH3N-NO

(22)

> CH * + N 0

(23)

3

CH3N-NO

3

2

NO u

2

CH .

°2

>

3

-> —^> N0

0 CH -

NO

N0

2

>

3

-> N0

HCHO + H0

(24)

2

2

2

> CH ON0 3

(25)

2

2

Another probable source of the r e l a t i v e l y high y i e l d of N 0 observed i n this experiment i s reaction of O H with the nitrosohydrazine: 2

NO ( C H

3

)

2

N - N ' K

+

OH

— >

( C H

3

)

2

N - N - N O

+

H 0 2

H


(26)

130

2V-NITROSO COMPOUNDS

(CH ) N-N-NO — > 3

2

(CH ) N* + N 0 3

2

2

(27)

Secondary product formation i s also expected to result from the reaction of OH with the nitramine, but the mechanism and products formed i n this case i s more uncertain.


Conclusions The results of the study reported here show clearly that, upon release into the atmosphere, Ν,Ν-dimethylhydrazine (UDMH) can be rapidly converted to N-nitrosodimethylamine by i t s reac tion with atmospheric ozone. A similar conclusion can be reached concerning nitrosamine formation from other unsymmetrically disubstituted hydrazines. Although nitrosamine and nitramine formation from UDMH (and s i m i l a r l y substituted hydrazines) w i l l probably be the major reaction pathway as long as the atmosphere into which the hydra zines are emitted contains some ozone (as does the "natural" troposphere), our results indicate that different products would potentially be formed i f these compounds are emitted into p o l l u ted atmospheres where 0 i s suppressed by high levels of NO. Under these conditions, although nitrosamine formation appears to occur to some extent, formation of an unknown product (or set of products) i s also observed. On the basis of mechanistic considerations we believe this product to be primarily a nitrosohydrazine. Upon photolysis, this compound may give r i s e to an N-nitrohydrazine, or, when 0 i s present, to the nitrosamine. The t o x i c i t y of nitrosohydrazines and nitrohydrazines are unknown, but i t seems unlikely that they are innocuous compounds. Although the results obtained have been useful i n i n d i c a t ing the major atmospheric fate of UDMH and similar hydrazines, this study must be considered to be largely exploratory i n nature. Additional work i s required to obtain more quantitative data under a wider variety of reaction conditions i n order to provide a firmer basis upon which to establish the assumed mechanism. Such studies are now underway i n our laboratory. 3

3

Acknowledgments The authors wish to gratefully acknowledge the valuable assistance of Mr. Richard Brown i n conducting the experiments. Helpful discussions with Dr. Daniel Stone, project o f f i c e r , and Lt. Col. Michael MacNaughton, project manager, are also acknow ledged. This study was supported by funds from the U.S. A i r Force Contract No. AF-F08635-78-C-0307.


8.

CARTER ET AL.

Formation of Ή-Nitrosodimethylamine

131

Literature Cited 1. 2.


3.

4.

5.

6.

7. 8. Pitts,

9. 10. 11. 12. 13. 14. 15. 16.

International Agency for Research on Cancer, Monographs on the Evaluation of Carcinogenic Risk to Man, V o l . 4, p. 137144, 1974. Urry, W. H.; Olsen, A. L.; Bers, E. M.; Krause, H. W.; Ikoku, C.; Gaibuez, A. "Autooxidation of 1,1-Dimethylhydraz i n e , " NAVEWEPS Report 8798, NOTS Technical Publication 3903, September 1965. Loper, G. L. "Gas Phase Kinetic Study of A i r Oxidation of UDMH," in Proceedings of the Conference on Environmental Chemistry of Hydrazine Fuels, Tyndall AFB, 13 September 1977, Report No. CEEDO-TR-78-14, 1970, p. 129. Stone, D. A. "The Vapor Phase Autooxidation of Unsymmetrical Dimethylhydrazine and 50 Percent Unsymmetrical Dimethylhydrazine-50 Percent Hydrazine Mixtures," Report No. ESL-TR80-21, A p r i l 1980. P i t t s , Jr., J . N . ; Tuazon, E. C.; Carter, W. P. L . ; Winer, A. M.; Harris, G. W.; Atkinson, R.; Graham, R. A. "Atmo spheric Chemistry of Hydrazines: Gas Phase Kinetics and Mechanistic Studies," F i n a l Report, U.S. A i r Force Contract No. F08635-78-C-0307, July 31, 1980. Tuazon, E. C . ; Carter, W. P. L . ; Winer, A. M . ; Pitts, J r . , J . N. "Reactions of Hydrazines with Ozone under Simulated Atmospheric Conditions," Environ. S c i . Technol., i n press, 1981. Doyle, G. J.; Bekowies, P. J.; Winer, A. M.; Pitts, Jr., J . N. Environ. S c i . Technol., 1977, 11, 45. Winer, A. M . ; Peters, J . W.; Smith, J . P . ; Pitts, Jr., J . N. Environ. S c i . Technol., 1974, 1118. Tuazon, E. C.; Winer, A. M.; Graham, R. Α.; Schmid, J . P . ; Jr., J . N. Environ. S c i . Technol., 1978, 12, 954. P i t t s , Jr., J . N . ; Grosjean, D . ; Van Cauwenberghe, K . ; Schmid, J . P . ; Fitz, D. R. Environ. S c i . Technol., 1978, 12, 946. Stockwell, W. R.; Calvert, J . G. J . Photochem., 1978, 8, 193. Lesclaux, R.; Demissy, M. Nov. J . Chemie., 1977, 1, 443. Lindley, C. R. C.; Calvert, J . G . ; Shaw, J . H. Chem. Phys. L e t t . , 1979, 67, 57. Peterson, J . T. "Calculated Actinic Fluxes (290-700 nm) for Air P o l l u t i o n Photochemistry A p p l i c a t i o n , " GVA 600/4-76-025, 1976. NASA Panel for Data Evaluation, "Chemical Kinetic and Hydrochemical Data for Use in Stratospheric Modeling," Evaluation Number 2, JPL Publication 79-27, A p r i l 1979. Harris, G. W.; Atkinson, R.; Pitts, Jr., J . N. J . Phys. Chem., 1979, 83, 2557.

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August 10, 1981.


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